Solar Storms Smack a Comet

This image of comet 153P/Ikeya-Zhang, taken by skywatcher Gilbert Jones on March 11, 2002, shows its ion tail decimated by a run-in with a coronal mass ejection (CME) from the Sun.Credit: Gilbert Jones/Three Buttes Observatory.

Astronomers
have pieced together what
appears to be the first direct evidence that solar storms can wreak
havoc with comets, destroying the ion tails of icy wanderers in a collision
of highly charged particles.

But the effect is not permanent and may serve as
a marker for scientists trying to track solar storms known as coronal mass
ejections (CMEs) as they blow out into space.

"What we
have now is sort of a new tool of tracking these ejections," said Geraint Jones,
co-investigator of the comet study and a researcher at NASA's Jet Propulsion Laboratory. "It's like dropping paint into
a flowing river of water."

The ion tails of comets constantly stream away from
the Sun, pushed back by solar wind blowing at about 894,774 mph (400 kilometers
per second). But the charged particles of CMEs, among the worst of
solar storms, can slam into a comet's ion tail at about 2.2 million
mph (1,000 kilometers per second), causing kinks, scalloped patterns or
disrupting the tail altogether, Jones' research found.

"We're still far from having a full understanding of
what's going on [with CMEs]," Jones told SPACE.com.

But by watching comet tail behavior, researchers
could learn more about changes in CME structure and speed as they
move through space, researchers added.

"When [CMEs] move outward we know there's a lot of
change, but that's it," explained Douglas Biesecker, a physicist with the
Space Environment Center at the National Oceanic and Atmospheric Administration
(NOAA). "It would be a little more useful if there were a lot more comets out
there."

The study, conducted by Jones and his colleague
John Brandt at the University of New Mexico, appeared in the online version
of the journal Geophysical Research Letters and
will appear in the journal's upcoming print edition.

Comet distortion

At the heart of Jones' study is
the comet 153P/Ikeya-Zhang, which passed through the inner solar system during spring 2002.

Jones and Brandt were able to identify specific
interactions between CMEs and Ikeya-Zhang's ion tail by combining data
from the sun-watching NASA/European Space Agency SOHO spacecraft and observations
collected by amateur astronomers.

CME events recorded by SOHO instruments on March 2, March 9-10 and
April 17 appear to have slammed into Ikeya-Zhang's ion tail each about a day or
so after leaving the Sun. None of the CMEs distorted the comet's tail for more
than an hour.

"On their own, the images were fascinating,"
Jones said. "But it was only when we put them all together that we saw how the
changes were occurring that we realized what was happening."

Past observations had suggested that CMEs
belched from the Sun could impact a comet's ion tail, including some stunning images
taken by the SOHO spacecraft last year.

During February 2003, SOHO caught the comet C/2002 V1
NEAT swing by the Sun during a CME event, which researchers believed caused a
kink in the icy wanderer's tail. The catch was a
fortunate one, since NEAT's orbit brought it close to the Sun in
astronomical terms, about one-tenth the distance between the Earth and the star
or 0.1 astronomical unit (AU). One AU is
about 93 million miles (150 million kilometers).

But Ikeya-Zhang's closest approach was about five
times farther out at 0.51 AU at a distance where sun-watching spacecraft
like SOHO can't see.

"Our studies
have been limited in the past because we're limited to observations from
spacecraft that are just measuring what the solar activity is near
the Sun," Jones said.

Some instruments,
such as the Solar Mass Ejection Imager aboard the Coriolis spacecraft in
Earth orbit and the planned STEREO observatories are seeking a wider view
on CMEs, Biesecker added.

Amateur assets

Part of the
success behind the Jones-Brandt study is due to the readily available
network of amateur
astronomers from around the world, which heeded an open call for
observations when Ikeya-Zhang swung past the Sun.

"Without
the amateur astronomers, this research would not have been possible," Jones
said. "It's a great example of how amateur astronomers and professionals can
work together."

Jones hopes that cooperation
will be repeated with a pair of comets that were observed earlier this
year.

"They have more telescope time to themselves than we have
sometimes as professional astronomers," said Biesecker of amateur
skywatchers.